ELEMENTS OF OBGANIZED STBUCTUBE. 245 



apple or tomato, we are able, by means of a low magni- 

 fier, to distinguish the cells of which it almost entirely 

 consists. Fig. 28 represents a bit of the flesh of a ripe 

 pippin, magnified 50 diameters. The cells mostly cohere 

 together, but readily admit of separation. 



Structure of the Cell. By the aid of the micro- 

 scope it is possible to learn something with regard to the 

 internal structure of the cell itself. Fig. 29 exhibits the 

 appearance of a cell from the flesh of the Artichoke 

 (Helianthus), magnified 230 diameters ; externally the 

 membrane, or wall of the cell, is seen in section. This 

 membrane is filled and distended by a 

 transparent liquid, the sap or free water 

 of vegetation. Within the cell is ob- 

 served a round body, b, which is called 

 the nucleus, and upon this is seen a 

 smaller nucleolus, c. Lining the inte- 

 rior of the cell-membrane and connected 

 with the nucleus, is a yellowish, turbid, 

 semi-fluid substance of mucilaginous 

 consistence, a, which is designated the protoplasm, or 

 formative layer. This, when more highly magnified, is 

 found to contain a vast number of excessively minute 

 granules. 



By the aid of chemistry the microscopist is able to dis- 

 sect these cells, which are hardly perceptible to the 

 unassisted eye, and ascertain to a good degree how they 

 are constituted. On moistening them with solution of 

 iodine, and afterward with sulphuric acid, the outer 

 membrane the cell-wall shortly becomes of a fine blue 

 color. It is accordingly cellulose, the only vegetable 

 substance yet known which is made blue by iodine after, 

 and only after, the action of sulphuric acid. At the 

 same time we observe that the interior, half -liquid, pro- 

 toplasm, coagulates and shrinks together, separates, 

 therefore, from the cell-wall, and, including with it the 



